Para-(2-hydroxyalkyloxy)styrene monomers and oligomers, such as p-(2-hydroxyethoxy)styrene (pHES) and oligomers thereof, are well known compounds that have various applications as monomers. For example, p-(2-hydroxyalkyloxy)styrene monomers and oligomers are useful as monomers for the preparation of cross-linked polymer solid electrolytes (Nakanishi et al., U.S. Pat. No. 6,096,234), poly(ethylene glycol)-coated polystyrene nanoparticles (Chen et al., J. Polym. Sci. Part A, Polym. Chem. 37:2155–2166 (1999)), polymeric solid phase supports used for the synthesis of organic molecules (Sutherland et al., WO 03/025033), polymers for use as organic binders in electrically conductive pastes (Yamamoto et al., U.S. Pat. No. 5,156,771), polymers for the treatment of metal surfaces to prevent corrosion (Kodama et al., U.S. Pat. No. 5,246,507), as well as other applications.
Although various methods for preparing p-(2-hydroxyalkyloxy)styrene monomers and oligomers are known, these methods are not commercially feasible for large-scale production because they use starting materials that are difficult to work with or involve multistep reactions that are not performed in a single reaction vessel. For example, Inokuma et al. (Heterocycles 40:401–411 (1995)) describe the preparation of pHES by reacting para-hydroxystyrene (pHS) with 2-chloroethanol in aqueous sodium hydroxide solution. Mori et al. (J. Polym. Sci. Part A, Polym. Chem. 28:551–558 (1990)) describe the preparation of pHES from pHS. In that method, the pHS is first reacted with β-bromoethyl acetate under basic conditions to form p-(β-acetoxyethoxy)styrene, which is then treated with alkaline methanol to form pHES. The methods described in both of those disclosures use pHS as a starting material, which has several disadvantages. Para-hydroxystyrene is only available as a 10% by weight solution in propylene glycol from non-bulk commercial sources. This low initial concentration makes it difficult to use for scale-up purposes. Moreover, the use of pHS is complicated because it readily decomposes, is toxic via skin absorption, and it readily polymerizes.
Chen et al., supra describe a method for preparing p-(2-hydroxyethoxy)styrene oligomers from p-chloromethylstyrene and hydroxy group-terminated poly(ethylene glycol). In that method, p-chloromethylstyrene is mixed with sodium hydride in THF for 2 hours. Then, a hydroxy group-terminated poly(ethylene glycol) is added. The use of p-chloromethylstyrene as starting material has many of the disadvantages given above for pHS.
Inokuma et al. (Heterocycles 54:123–130 (2001)) describe the preparation of p-(2-hydroxyethoxy)styrene monomer and oligomers from a reaction utilizing oligoethyleneglycol mono(p-bromophenyl) ethers, tributylvinylstannane, and 2,6-di-tert-butyl-4-methylphenol in the presence of a tetrakis(triphenylphosphine) palladium catalyst.
Sutherland et al. supra describe a two-step procedure for preparing p-(2-hydroxyethoxy)styrene oligomers. In the first step, an oligo(ethylene glycol) ether is reacted with tosyl chloride to form the mono-tosyl-oligo(ethylene glycol) ether. In the second step, the isolated mono-tosyl-oligo(ethylene glycol) ether is reacted with p-acetoxystyrene to give the p-(2-hydroxyethoxy)styrene oligomer.
Woods et al. (U.S. Pat. No. 5,019,629) describe a two-step procedure for preparing p-(2-hydroxyethoxy)styrene starting with p-hydroxybenzaldehyde. In the first step, p-(2-hydroxyethoxy)benzaldehyde is formed by reacting p-hydroxybenzaldehyde with ethylene carbonate in the presence of potassium carbonate. In the second step, p-(2-hydroxyethoxy)styrene is formed by reacting the isolated p-(2-hydroxyethoxy)benzaldehyde with methyltriphenylphosphonium bromide in the presence of sodium amide.
Ueno et al. (U.S. Pat. No. 6,340,759) also describe a two-step procedure for preparing p-(2-hydroxyethoxy)styrene starting with p-hydroxybenzaldehyde. In the first step, p-(2-hydroxyethoxy)benzaldehyde is formed by reacting p-hydroxybenzaldehyde, sodium hydride, and (2-bromoethoxy)-tert-butyldimethylsilane. In the second step, p-(2-hydroxyethoxy)styrene is formed by reacting the isolated p-(2-hydroxyethoxy)benzaldehyde with (ethyl)triphenylphosphonium bromide in the presence of sodium hydride.
Sheehan et al. (U.S. Pat. No. 5,087,772) describe a method for preparing p-hydroxystyrene by reacting p-acetoxystyrene with a suitable alcohol in the presence of a catalytic amount of base. The preparation of p-(2-hydroxyalkyloxy)styrene monomers and oligomers is not described in that disclosure.
Methods for alkoxylating a phenolic substrate are known. Parker et al. (Macromolecules 34:2048–2059 (2001)) describe a process for the synthesis of dimethyl 5-(2-hydroxyethoxy)isophthalate by reacting dimethyl 5-hydroxyisophthalate with ethylene oxide in the presence of sodium methoxide. Rayborn (U.S. Pat. No. 6,111,146) describes the alkoxylation of an alkylphenol with an alkylene oxide using a base catalyst. Neither of those disclosures describes the preparation of p-(2-hydroxyalkyloxy)styrene monomers and oligomers in a single vessel reaction via a base-catalyzed reaction of a styrene ester, a suitable alcohol and an alkylene oxide.
The problem to be solved, therefore, is the need for an economical method for the large-scale, commercial production of p-(2-hydroxyalkyloxy)styrene monomers and oligomers. Additionally, the method should utilize starting reagents that are readily available and are stable and less toxic than those currently known in the art.
Applicants have solved the stated problem by discovering a method for producing p-(2-hydroxyalkyloxy)styrene monomers and oligomers via a base-catalyzed reaction of a styrene ester, a suitable alcohol and an alkylene oxide in a single vessel reaction.